41.2 Kidneys and osmoregulatory organs - Biology 2e | OpenStax (2023)

learning objectives

By the end of this section, you will be able to:

  • Explain how the kidney functions as the most important osmoregulatory organ in mammalian systems
  • Describe the structure of the kidney and the function of the parts of the kidney
  • Describe how the nephron is the functional unit of the kidney and explain how it actively filters blood and produces urine
  • Explain in detail the three steps of urine formation: glomerular filtration, tubular reabsorption, and tubular secretion

Although the kidneys are the primary osmoregulatory organs, the skin and lungs also play a role in the process. Water and electrolytes are lost through sweat glands in the skin, which help to moisten and cool the surface of the skin, while small amounts of water are removed from the lungs by mucus secretion and water vapor evaporation.

Kidneys: the main osmoregulatory organ

this herekidney, as the picture showsFigure 41.4, are a pair of bean-shaped structures located just below and behind the liver in the abdominal cavity. On top of each kidney is an adrenal gland, also called the adrenal gland. The kidneys filter and clean the blood. All the blood in the body is filtered through the kidneys several times a day; these organs consume almost 25% of the oxygen absorbed through the lungs to perform this function. Oxygen allows kidney cells to efficiently produce chemical energy in the form of ATP through aerobic respiration. The filtrate from the kidney is calledUrine.

41.2 Kidneys and osmoregulatory organs - Biology 2e | OpenStax (1)

number41,4 The kidneys filter the blood to produce urine, which is stored in the bladder before being excreted through the urethra. (Source: NCI paper modification)

kidney structure

Externally, the kidney is surrounded by three layers, as shownFigure 41.5.The outermost layer is the hard layer of the so-called connective tissuerenal fascia.The second layer is calledperirenalni fedtsæk, which helps keep the kidney in place. The third and innermost layer isrenal capsuleInternally, the kidney is divided into three regions - the outer regioncortex, Amarrowin the middle, irenal pelvisinvited tohilumkidney. The hilum is the bean-shaped depression where blood vessels and nerves enter and exit the kidney; it is also the exit point for the ureters. The renal cortex is granular due to the presence ofnephron- Functional unit of the kidney. The medulla is made up of several pyramidal tissue masses, the so-calledmypyramid.The space between the pyramids is calledrenal columnwhere the blood vessels pass. The top of the pyramid is called the renal papilla and points to the renal pelvis. Each kidney has an average of eight renal pyramids. The renal pyramid together with the adjacent cortical area is calledtrump.Renal pelvis leads toureteroutside the kidneys. Inside the kidney, the renal pelvis branches into two or three extensions called the macronephrongoblet, further branching into small cups. The ureter is the tube of urine that leaves the kidney and enters itbladder.

(Video) CH.41-Chemical signal an animals, Part2

visual connection

visual connection

41.2 Kidneys and osmoregulatory organs - Biology 2e | OpenStax (2)

number41,5 It shows the internal structure of the kidney. (Source: NCI paper modification)

Which of the following statements about the kidneys is false?

  1. The renal pelvis empties into the ureter.
  2. The renal pyramid is located in the medulla.
  3. Capsules covered with leather.
  4. Nephrons are located in the renal cortex.

Because the kidney filters blood, its network of blood vessels is an important part of its structure and function. Arteries, veins and nerves that supply blood to the kidneys enter and exit the hilum. The kidney's blood supply begins with the branching of the aorta intorenal artery(each named after the area of ​​the kidney through which it passes) and ends with an outletminetaking partinferior vena cavaThe renal artery is divided into severalSegmental arteriesAfter entering the kidney. Each segmental artery is further divided into severalinterlobar arteryand enters the renal columns that supply the kidney lobes. The interlobar arteries split and form at the junction of the renal cortex and medullaarcuate arteryThe arcuate "arc" arteries run along the base of the medullary pyramid.skin radial arteries, as the name suggests, radiates from the arcuate artery. Cortical efferent arteries branch into many afferent arterioles, which then enter the capillaries that supply the nephrons. Veins run alongside arteries and have a similar name except without segmental veins.

As mentioned earlier, the functional unit of the kidney is the nephron as shown in the diagramFigure 41.6.Each kidney consists of more than 1 million nephrons that are interspersed with the renal cortex and appear granular when cut sagittally. There are two types of nephrons –cortical nephron(85%), which is located deep in the kidney cortex, andnephron medulla(15%), in the renal cortex next to the renal medulla. A nephron consists of three parts –Renal corpuscles, Anyretubuli, and the associated capillary network, originate from the cortical radial arteries.

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41.2 Kidneys and osmoregulatory organs - Biology 2e | OpenStax (3)

number41,6 The nephron is the functional unit of the kidney. Glomeruli and convoluted tubules are located in the cortex of the kidney, while the collecting ducts are located in the pyramids of the medulla. (Source: NIDDK Job Change)

Which of the following statements about nephrons is false?

  1. The collecting duct joins the distal convoluted tubule.
  2. Bowman's capsule surrounds the glomerulus.
  3. The loop of Henle is located between the proximal and distal convoluted tubules.
  4. The loop of Henle empties into the distal convoluted tubule.

Renal corpuscles

The renal corpuscles, located in the renal cortex, consist of a network called capillariesGlomerulusand the capsule, the cup-shaped chamber that surrounds it called the glomerulus orBowman's capsule.


Renal tubules are long, complex structures that emerge from the glomerulus and are divided into three parts based on function. The first part is the so-calledProximal convoluted tubule (PCT)Due to its proximity to the glomerulus, it remains in the kidney cortex. The second part is the so-calledRing of Henle, or the nephritic cycle, since it forms a cycle (sarefuseilift) through the renal medulla. The third part of the renal tubule is calledDistal convoluted tubule (DCT)And this part is also limited to the cortex of the kidney. The DCT is the posterior part of the nephron that connects and empties its contents into the collecting ducts that line the pyramid of the medulla. Collecting ducts collect contents from multiple nephrons and join as they enter papillae in the medulla of the kidney.

Capillary network in the nephron

A network of capillaries originating from the renal arteries supplies the nephrons with filtered blood. The branch that enters the glomerulus is calledafferent arterioles.The branch that leaves the glomerulus is calledefferente arteriole.In the glomerulus, the network of capillaries is called the glomerular capillary bed. When the efferent arteriole leaves the glomerulus, it is formedPeritubular capillary network, which surrounds part of the renal tubule and interacts with it. In cortical nephrons, a network of peritubular capillaries surrounds the PCT and DCT. In the medullary nephron, the peritubular capillary network forms a network around the so-called loop of Henle.straight blood vessels.

study link

study link

to gothis websiteSee another coronary section of the kidney and explore animations of nephrons in action.

Kidney function and physiology

The kidneys filter the blood in three stages. First, the nephron filters the blood flowing through the glomerular capillary network. Almost all solutes, except proteins, are filtered by a process called the glomerulusglomerular filtration.Secondly, the filtrate collects in the renal tubules. Most solutes are reabsorbed through a process called PCTtubular reabsorption.In the loop of Henle, the filtrate continues to exchange solutes and water with the renal medulla and the peritubular capillary network. Water is also reabsorbed during this step. Additional solutes and waste products are then excreted in the renal tubulesrenal tubular secretion, which is essentially the opposite process of renal tubular reabsorption. Collecting tubules collect the filtrate from the nephron and merge into medullary papillae. From here, the mastoids carry the filtrate (now called urine) into the small renal calyces, which eventually connect to the ureters through the renal pelvis. The whole process is shown in the pictureFigure 41.7.

41.2 Kidneys and osmoregulatory organs - Biology 2e | OpenStax (4)

number41,7 Each part of the nephron performs a different function by filtering waste and maintaining homeostasis. (1) The glomerulus expels small solutes from the blood through pressure. (2) The proximal convoluted tubule reabsorbs ions, water, and nutrients from the filtrate into the interstitial fluid and actively transports toxins and drugs from the interstitial fluid into the filtrate. The proximal tubule also selectively secretes ammonia (NH3) into the filtrate where it reacts with H+Obrazac NH4+.The more acidic the filtrate, the more ammonia is excreted. (3) Descending loop of Henle cells containing aquaporins that allow water to pass from the filtrate to the interstitial fluid. (4) Detail of the ascending ring of Henle, Na+i klor-Ions diffuse into the interstitial fluid. In thicker parts, these same ions are actively transported into the interstitial fluid. Since it is the salt that is lost instead of the water, the filtrate becomes more and more dilute as it moves up. (5) In the distal convoluted tubule, K+i+Ions are selectively excreted in the filtrate, while Na+, claws-i HCO3-Ions are reabsorbed to maintain blood pH and electrolyte balance. (6) The collecting duct reabsorbs the solute and water in the filtrate to form dilute urine. (Source: NIDDK Job Change)

glomerular filtration

Glomerular filtration removes most solutes due to high blood pressure and specialized membranes in the afferent arterioles. Blood pressure in the glomerulus is maintained independently of factors affecting systemic blood pressure. "Leaky" connections between endothelial cells in the glomerular capillary network allow easy passage of solutes. Except for macromolecules such as proteins, all solutes pass through the glomerular capillaries by passive diffusion. This stage of the filtration process has no energy requirements.glomerular filtration rate (GFR)is the amount of glomerular filtrate produced by the kidneys per minute. GFR is regulated by several mechanisms and is an important indicator of kidney function.

study link

study link

For more information on the renal vasculature, clickthis reviewand blood flow stage.

tubular reabsorption and secretion

Tubular reabsorption occurs in the PCT part of the tubule. Almost all nutrients are reabsorbed, which occurs by passive or active transport. Reabsorption of water and some important electrolytes is regulated and can be influenced by hormones. Sodium (Na+) is the most abundant ion, most of which is reabsorbed by active transport and transferred to peritubular capillaries. Because of Na+Actively transported from the tubules, water follows to equalize the osmotic pressure. Water is also independently reabsorbed in the peritubular capillaries due to the presence of aquaporins or water channels in the PCT. This occurs due to hypotension and hyperosmolarity in the peritubular capillaries. However, each solute has onetransport maxThe excess is not reabsorbed.

In the loop of Henle, the permeability of the membrane changes. The descending limb is permeable to water, not solutes; the ascending limb is the opposite. In addition, the loop of Henle penetrates the renal medulla, which is naturally rich in salt and readily absorbs water from the renal tubules, concentrating the filtrate. The osmotic gradient increases as it penetrates deeper into the medulla. Because the two sides of the loop of Henle perform opposite functions, as shownFigure 41.8, which acts as aupstream multiplier.Vasa recta around it acts ascounter current exchanger.

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41.2 Kidneys and osmoregulatory organs - Biology 2e | OpenStax (5)

number41,8 The ring of Henler acts as an upstream multiplier that uses energy to create a concentration gradient. The drip branch is permeable. Water flows from the filtrate into the interstitial fluid, so as it falls into the renal medulla, the osmotic pressure within the limb increases. At the bottom, the osmotic pressure in the circulation is higher than in the interstitial fluid. Therefore, when the filtrate enters the ascending branch, Na+i klor-Ions leave through ion channels in the cell membrane. further up on+se aktivno transportira iz filtrata i Cl-as follows. Osmolality is measured in milliosmoles per liter (mOsm/L).

Loop diuretics are drugs that are sometimes used to treat high blood pressure. These drugs inhibit Na reabsorption+i klor-Ions produced by the ascending limb of the loop of Henle. The side effect is that they increase urination. Why do you think this happens?

By the time the filtrate reaches the DCT, most of the urine and solutes are reabsorbed. If the body needs extra water, all that water can be reabsorbed at this point. Further reabsorption is controlled by hormones, discussed in a later section. Excretion of waste is due to lack of reabsorption and tubular secretion. Unwanted products such as metabolic waste, urea, uric acid and certain drugs are excreted through renal tubular secretions. Most tubular secretion occurs in the DCT, but some occurs early in the collecting duct. The kidneys also maintain acid-base balance by excreting excess H2+ion.

Although the parts of the tubules are called proximal and distal, on a cross-section of the kidney, the tubules are close together and in contact with each other and the glomeruli. This allows the exchange of chemical messengers between different types of cells. For example, the ascending branch of the DCT loop of Henle has a large number of cells calledIntense point, which come into contact with cells called afferent arteriolesjuxtaglomerular cells.Macula compacta and juxtaglomeral cells together form the juxtaglombar complex (JGC). JGC is an endocrine structure that secretes reninase and erythropoietin. When hormones trigger plaque cells in the DCT due to changes in blood volume, blood pressure, or electrolyte balance, these cells can immediately communicate the problem to the capillaries of the afferent and efferent arterioles, which can contract or relax in response to changes in renal glomerular filtration rates.

Career connections

Career connections

nephrologistsNephrologists study and treat kidney diseases—both those that lead to kidney failure (such as diabetes) and those that result from kidney disease (such as high blood pressure). Changes in blood pressure, blood volume and electrolyte balance are the area of ​​expertise of nephrologists.

Nephrologists usually work with other doctors who refer patients to them or consult with them about specific diagnoses and treatment plans. Patients are often referred to a nephrologist for symptoms such as blood or protein in the urine, high blood pressure, kidney stones or kidney failure.

Nephrology is a subspecialty of internal medicine. To become a nephrologist, medical school is followed by further training to obtain a certificate in internal medicine. Another two years or more were devoted to the study of kidney disease and its accompanying effects on the body.


What are the kidneys and osmoregulatory organs? ›

The kidneys are bean-shaped organs that serve several essential regulatory roles in vertebrates. Besides removing urea and uric acid from the blood, the kidneys also help in maintaining the water and salt concentration in it. This process is called as osmoregulation.

What is osmoregulation in the kidney in biology? ›

Osmoregulation occurs in the medulla of the kidney and involves two key events: The loop of Henle establishes a salt gradient (hypertonicity) in the medulla. Anti-diuretic hormone (ADH) regulates the level of water reabsorption in the collecting duct.

How do kidneys contribute to osmoregulation? ›

The kidney is the main organ responsible for osmoregulation in the human body. It filters blood to remove excess water and dissolved substances, such as salts and urea, and then reabsorbs the necessary substances back into the bloodstream, while excreting the excess in the form of urine.

What two organs are responsible for osmoregulation? ›

Although the kidneys are the major osmoregulatory organ, the skin and lungs also play a role in the process.

What are examples of osmoregulatory organs? ›

6.1). Many structures and organs are involved in osmoregulation, including the skin, gills, digestive tract, kidneys, and bladder.

What do you mean by osmoregulatory organ? ›

Osmoregulation is a process that regulates the osmotic pressure of fluids and electrolytic balance in organisms. In animals, this process is brought about by osmoreceptors, which can detect changes in osmotic pressure. Humans and most other warm-blooded organisms have osmoreceptors in the hypothalamus.

What is osmoregulation examples? ›

Osmoregulators actively control salt concentrations despite the salt concentrations in the environment. An example is freshwater fish. The gills actively uptake salt from the environment by the use of mitochondria-rich cells.

What is osmoregulation and why is it important? ›

Human osmoregulation is the process of maintaining water and mineral balance in the body. Osmoregulation helps in maintaining a constant normal blood pressure. It is an important component of life as it maintains water and mineral balance at the cellular level.

What is an example of osmoregulation in biology? ›

It is the way by which an organism maintains suitable concentration of solutes and amount of water in the body fluids. An example employed by organisms is excretion (such as getting rid of metabolic wastes and other substances toxic to the body when they are in large amounts).

How do the kidneys help in osmoregulation and in maintaining homeostasis? ›

The kidneys maintain homeostasis by controlling the amount of water, ions, and other substances in the blood. Kidneys also secrete hormones that have other homeostatic functions.

How osmoregulation with the kidneys work to maintain homeostasis? ›

There is a constant input of water and electrolytes into the system. Excess water, electrolytes, and wastes are transported to the kidneys and excreted, helping to maintain osmotic balance. Insufficient fluid intake results in fluid conservation by the kidneys.

Why is osmosis important in the kidneys? ›

Keeping the body's conditions stable makes it possible for living things to survive. Osmosis plays an important role in the human body, especially in the gastro-intestinal system and the kidneys. Osmosis helps you get nutrients out of food. It also gets waste products out of your blood.

What are the benefits of osmoregulation? ›

Osmoregulation enables organisms to live in environments that osmoconformers cannot. Additionally, it allows marine organisms to maintain an osmolarity different from seawater. For example, sharks have an internal salt concentration much lower than that of seawater.

What is the osmosis of the kidneys? ›

Osmosis is a phenomenon of paramount significance for the transport of water and solutes through biological membranes. It accounts for fluid transport out of the kidney tubules and the gastrointestinal tract, into capillaries, and across cell membranes.

Which 3 systems of the body are important for osmoregulation? ›

The human excretory system functions to remove waste from the body through the skin as sweat, the lungs in the form of exhaled carbon dioxide, and through the urinary system in the form of urine. All three of these systems participate in osmoregulation and waste removal.

What is osmoregulation simple words? ›

osmoregulation, in biology, maintenance by an organism of an internal balance between water and dissolved materials regardless of environmental conditions.

What is an example of osmoregulation in the human body? ›

In humans, the kidney plays an important role in osmoregulation of body's internal environment. The body shows osmoregulation in two common ways or cases, dehydration and waterlogging. In case of dehydration, the hypothalamus gives the signal to the pituitary gland to secrete ADH (antidiuretic hormone).

How do you explain osmoregulation? ›

Osmoregulation is a homeostatic mechanism that regulates the optimum temperature of water and salts in the tissues and body fluids. It maintains the internal environment of the body through water and ionic concentration.

Why is osmoregulation and blood control important? ›

Osmoregulation and osmotic balance are important bodily functions, resulting in water and salt balance. This regulation equalizes the number of solute molecules across a semi-permeable membrane by the movement of water to the side of higher solute concentration.

What is one example of osmoregulation function of the kidney? ›

Kidneys: The Main Osmoregulatory Organ

Kidneys filter blood and purify it. All the blood in the human body is filtered many times a day by the kidneys; these organs use up almost 25 percent of the oxygen absorbed through the lungs to perform this function.

What are the different types of osmoregulation? ›

Two major types of osmoregulation are osmoconformers and osmoregulators.

How does osmoregulation maintain the balance of water in the body? ›

Osmoregulation is the control of water levels and mineral ions (salt) in the blood. Water levels and mineral ions in the blood are controlled to keep the concentrations the same inside the cells as around them. This protects cells by stopping too much water from entering or leaving them by osmosis.

What would happen without osmoregulation? ›

If osmoregulation fails and the body loses too much water (dehydration) the concentration of nutrients and waste products becomes too high which can cause the metabolic processes in cells to slow or stop; killing the organism.

How do kidneys use osmosis and diffusion? ›

In order to get water to leave the filtrate through diffusion, the area surrounding the nephron must have a high salt concentration. A high salt concentration in the interstitial fluid outside of the nephron will provide a driving force for osmosis, allowing water to be recovered from the filtrate.

What is an example of osmosis in everyday life? ›

  • When you keep raisin in water and the raisin gets puffed. ...
  • When we are suffering from severe sore throat we are advised to gargle salt water. ...
  • Plants take water and mineral from roots with the help of Osmosis.
  • If you are there in a bath tub or in water for long your finger gets pruned. ...
  • .

Where is water absorbed by osmosis in the kidney? ›

The proximal convoluted tubule (PCT) is a segment of the renal tubule responsible for the reabsorption and secretion of various solutes and water.

What system is most important for osmoregulation? ›

Osmoregulation is under the control of a single hormonal system, ADH, whereas volume regulation is under the control of a set of redundant and overlapping control mechanisms. Lack or excess of ADH results in defined and rather dramatic clinical syndromes of excess water loss or water retention.

What causes water on the kidneys? ›

Hydronephrosis is the swelling of a kidney due to a build-up of urine. It happens when urine cannot drain out from the kidney to the bladder from a blockage or obstruction.

How do kidneys remove water from blood? ›

A blood vessel runs alongside the tubule. As the filtered fluid moves along the tubule, the blood vessel reabsorbs almost all of the water, along with minerals and nutrients your body needs. The tubule helps remove excess acid from the blood. The remaining fluid and wastes in the tubule become urine.

What is excretory and osmoregulatory system? ›

Excretion can be defined as the process of removal or expulsion of waste from the cells of the body of living organisms. Osmoregulation is the process of maintaining a suitable concentration of salt and water across the membranes present within the body.

What organs are associated with the kidneys? ›

The organs of the urinary system include the kidneys, renal pelvis, ureters, bladder and urethra. The body takes nutrients from food and converts them to energy. After the body has taken the food components that it needs, waste products are left behind in the bowel and in the blood.

Why is kidney called osmoregulatory organ? ›

Kidneys regulate the osmotic pressure of a mammal's blood through extensive filtration and purification in a process known as osmoregulation. All the blood in the human body is filtered many times a day by the kidneys.

What is an example of osmoregulation? ›

It is the way by which an organism maintains suitable concentration of solutes and amount of water in the body fluids. An example employed by organisms is excretion (such as getting rid of metabolic wastes and other substances toxic to the body when they are in large amounts).

What are some examples of osmoregulation in humans? ›

In humans, the kidney plays an important role in osmoregulation of body's internal environment. The body shows osmoregulation in two common ways or cases, dehydration and waterlogging. In case of dehydration, the hypothalamus gives the signal to the pituitary gland to secrete ADH (antidiuretic hormone).

Why is osmoregulation important? ›

Human osmoregulation is the process of maintaining water and mineral balance in the body. Osmoregulation helps in maintaining a constant normal blood pressure. It is an important component of life as it maintains water and mineral balance at the cellular level.

What are the important roles of osmoregulation in carrying out essential life processes? ›

Introduction. Osmoregulation is a fundamental process of living systems, equivalent in importance to respiration, digestion, or reproduction. Osmoregulatory processes are those that enable a fish to maintain its cellular fluid composition and volume.

Why is osmoregulation important in the function of the excretory system? ›

Osmoregulation balances concentrations of solutes and water across semi-permeable membranes, maintaining homeostasis. Ions cannot diffuse passively through membranes; instead, their concentrations are regulated by facilitated diffusion and active transport.

What is the function of the kidneys in maintaining homeostasis? ›

The kidneys regulate circulatory volume by controlling sodium and water balance, thus maintaining extracellular fluid volume (ECFV) homeostasis. Simply put, an increase in sodium and water consumption leads to an increase in ECFV, which in turn increases blood volume.

How do the kidneys regulate the osmolarity of the blood and blood pressure? ›

The kidney regulates plasma osmolarity by modulating the amount of water, solutes, and electrolytes in the blood. It ensures long term acid-base balance and also produces erythropoietin which stimulates the production of red blood cell.

How the kidneys work? ›

Here's how kidneys perform their important work:

Blood enters the kidneys through an artery from the heart. Blood is cleaned by passing through millions of tiny blood filters. Waste material passes through the ureter and is stored in the bladder as urine. Newly cleaned blood returns to the bloodstream by way of veins.


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